Aggregated diamond nanorod

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Stereomicroscopy image of an ADNR sample (diameter ~2 mm)

Aggregated diamond nanorods, or ADNRs (also called a hyperdiamond), are a nanocrystalline form of diamond believed to be the hardest and least compressible known material, as measured by their isothermal bulk modulus: aggregated diamond nanorods have a modulus of 491 gigapascals (GPa), while a conventional diamond has a modulus of 442 GPa.[1] ADNRs are also 0.3% denser than regular diamond. The ADNR material is also harder than type IIa diamond and ultrahard fullerite.

A <111> surface (normal to the largest diagonal of a cube) of pure diamond has a hardness value of 167 GPa (±6) when scratched with a nanodiamond tip, while the nanodiamond sample itself has a value of 310 GPa when tested with a nanodiamond tip.[2] However, the test only works properly with a tip made of harder material than the sample being tested. This means that the true value for nanodiamond is likely somewhat lower than 310 GPa.

ADNRs are produced by compressing fullerite powder — a solid form of allotropic carbon fullerene — with two somewhat similar methods. One uses a diamond anvil cell and applied pressure ~37 GPa without heating the cell.[3] In another method, fullerite is compressed to lower pressures (2-20 GPa) and then heated to a temperature in the range 300-2500 K.[4][5][6][7] Extreme hardness of nanodiamonds was reported by numerous researchers in the 1990s.[2][3][8] The material is a series of interconnected diamond nanorods, with diameters of between 5 and 20 nanometres and lengths of around 1 micrometre each.

[edit] See also

[edit] References

  1. ^ Aggregated Diamond Nanorods, the Densest and Least Compressible Form of Carbon
  2. ^ a b V. Blank et al. "Ultrahard and superhard phases of fullerite C60: comparison with diamond on hardness and wear" Diamond and Related Materials 7 (1998) 427 free download
  3. ^ a b V. Blank et al. "Is C60 fullerite harder than diamond?" Physics Letters A 188 (1994) 281
  4. ^ M. E. Kozlov et al. "Superhard form of carbon obtained from C60 at moderate pressure" Synthetic Metals 70 (1995) 1411
  5. ^ V.D. Blank et al. "Ultrahard and superhard carbon phases produced from C60 by heating at high previous termpressure: structural and Raman studies" Physics Letters A 205 (1995) 20
  6. ^ H. Szwarc et al. "Chemical modifications of C60 under the influence of pressure and temperature: from cubic C60 to diamond" Synthetic Metals 77 (1996) 26
  7. ^ V. D. Blank et al. "Phase transformations in solid C60 at high-pressure-high-temperature treatment and the structure of 3D polymerized fullerites" Physics Letters A 220 (1996) 149
  8. ^ T. Irifune, A Kurio, S. Sakamoto, T. Inoue, H. Sumiya "Ultrahard polycrystalline diamond from graphite" Nature 421 (2003) 599

[edit] External links

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